1. Field of the Invention
The present invention relates to robots for transferring workpieces such as semiconductor wafers between process tools or a process tool and workpiece storage location, and in particular to a precision workpiece handling robot having a robust, scalable and easily configured design.
2. Description of Related Art
The introduction of workpiece handling robots into the semiconductor fabrication process represented a significant advance in automation over manual and early transfer equipment for moving wafers between various process tools and/or workpiece storage locations. It is an important feature of conventional workpiece handling robots to be able to quickly and precisely access a workpiece from a first position, deliver it to a new location having different X, Y and Z coordinates in Cartesian space, and set it down without risk of damage to the workpiece.
In order to accomplish this, a typical robot includes a central mast mounted in a base for translation along a vertical axis. A proximal arm, or link, is rotatably mounted to an upper end of the mast, and a distal arm, or link, is rotationally mounted to the opposite end of the proximal link. The wafer handling robot further includes an end effector pivotally attached to the distal link for supporting the workpiece. Various motors are further provided, conventionally mounted in the base, for translating the central mast, and for rotating the proximal and distal links such that the end effector may be controllably maneuvered in three-dimensional space. In particular, the central mast conventionally comprises a pair of overlapped concentric shafts. A first motor is provided in the base to vertically translate the shafts, a second motor is provided in the base for rotating the proximal link via the outer shaft, and a third motor is provided in the base for rotating the distal link via the inner shaft.
In transporting workpieces such as semiconductor wafers and flat panel displays, it is important that the robot precisely locate the end effector at a desired position with respect to a workpiece to be accessed and/or a location where the workpiece is to be set down. With current wafer storage and transfer systems, an error of even xe2x85x9xe2x80x3 in the expected position of the end effector could result in damage or ruin to a workpiece which may be worth thousands of dollars. Moreover, even a minor positioning error in the central shaft, links or motors may result in a significantly larger positioning error by the time the error is carried through to the end effector.
It is difficult to design a robot capable of meeting these precise tolerances and performance requirements. While such robots are known, they employ sophisticated mechanisms which are expensive to implement and difficult to maintain. A further disadvantage to such robots is that they are generally built to precise specifications, and it is not possible to vary, or scale, the length of the various components or overall size of the robot without sacrificing positional accuracy and performance. This is a significant limitation in that different applications often require differently sized components. For example, 200 mm and 300 mm wafer fabrications require significantly different positioning requirements for a wafer handling robot. It is therefore desirable to be able to scale the length of the base and/or mast for a greater vertical stroke, as well as to be able to scale the links for a greater horizontal reach.
It is therefore an advantage of the present invention to provide a wafer handling robot capable of precise positional accuracy and repeatability.
It is a further advantage of the present invention to provide a wafer handling robot with a simple design and low number of parts to facilitate easy configuration and maintenance.
It is another advantage of the present invention to provide a wafer handling robot with a large mean time between failure.
It is a still further advantage of the present invention to provide a wafer handling robot with scalable components.
It is a further advantage of the present invention to provide a sealed robot capable of operating in hostile environments and capable of maintaining an environment different than that surrounding the robot.
These and other advantages are provided by the present invention which in general relates to an improved wafer handling robot for transporting workpieces such as semiconductor wafers and flat panel displays between process tools and/or workpiece storage locations within a wafer fab. The robot includes a base comprising a rigid backbone for providing a significant degree of structural stability to the robot. The base further includes a mast, a linear drive system for translating the mast, and a shoulder drive system for rotating the mast. The shoulder drive system includes a harmonic drive reduction system for providing a stiff, smooth and precise output rotation of the mast section. The various components included within both the linear and shoulder drive systems are preassembled into the motors to provide a unitized design. This feature allows the motors to be quickly and easily installed within the base during configuration of the robot.
The robot further includes a proximal link fixedly mounted to the mast for rotation with the mast, and a distal link rotatably mounted to the proximal link. An end effector for supporting various workpieces is rotationally mounted to the distal end of the distal link. An elbow drive is mounted to the proximal link, extending down into the mast section, for driving rotation of the distal link with respect to the proximal link. Torque is transmitted from the elbow drive to the distal link by steel straps wrapped around a drive pulley from the elbow drive and a driven pulley in the distal link. Similarly, torque is transmitted from the distal link to the end effector via a second set of steel straps wrapped around pulleys provided in the distal link and end effector, respectively.
The robot according to the present invention is capable of precisely positioning the end effector of the robot at a desired location, while at the same time having a simple, robust and easily maintained design. Moreover, the various components of the robot are scalable to different sizes to handle 200 mm and 300 mm requirements, as well as other applications.